Radiosignaling system



E. F. W.' LEXANDEHSN.

RADISIGNALING SYSTEM.

Wulf/mow mio SEPT. 4, 191 7.

Pnene Aug. 3 SHEETSAHEU z.

f6 Inventor Ernst F`. W. D l exandersom bwl@ His DTttorneg 3 SHETSw--SHEET 3.

Patenfe-d Aug.

E. F. W. MEXANUERSON.

ADISEGNAUJG SYSTEM.

/MLICATIQN mm SEPI, 4. 1917. lAQGfi/l,

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ERNST F. W. ALEXANDRSON, 0F SCEENECTADY, NEW`YORK, ASSIGNOR T0 GENERAL A l ELECTRIC COMZPANY, A CORPORATION OF NEW YORK.

' BADIOSIGNALING SYSTEM.

Patented' Aug. 22,' 192e.

Application led September 4, 1917. Serial No. 189,495.

To all whom it may concern.'

Be it known that I, ERNST F. W. ALEXAN- nnRsoN, a citizen of the United States, re?V 4siding at Schenectady, in the county of Sche nectady, State of New York,`have invented 'certain new and useful Improvements in Radiosignaling Systems, of which the fol-A lowing is a specification.

My present invention Arelates to-radio signaling systems and comprises both transmitting and receiving apparatusifor use in4 such systems. Y

One ofthe objects of my inventionis to provide a system of multiplex "signaling in whichl a plurality .of messages may be transmitted and received simultaneously by the use of a single wave length. y A

A second `object of my invention is to provide a systemgfor transmitting and receiving messages which is arranged in such a way that it will be practically impossible for another station to interfere Awith the eiicient -transmission and reception of the de-l sired messages.

` source `of supply, p v

sations of a desired frequency and of sub-I Still another object of my invention is to.

provide a system whereby messages may be transmitted between two stations 1n such a way that it will not be possible for a thirdV station to receive them.

In attaining the above objects, for transmitting purposes, asource of continuousv radio frequency current, such, for example, as a high frequency alternator, an arc generator' or/an electron discharge oscillator. I control the current in the antenna which-` is supplied by this source by means of a magnetic amplifier of the general type described in my prior Patent #1,206,643. By varying the controlling cur'- rent supplied to the, windings of this amplifier at a frequency lower than that,of the I produce amplitude pulstantially sine wave form in the current supplied to the antenna.l y ,l

If it is merely desired to transmit s1mul taneously a plurality of different messages, I supply tov the controlling-windings ofthey amplifier currents'of as many different lower frequencies as the number .of messages which it' is desired to transmit, these currents being supplied only during the intervals nec,L

essary tol form the dots yand Idashes for each message. It will, of course, be apparent that in case several messages are being sent si.

`multaneously, the amplitude I employ, i

pulsations produced in the fundamental wave willbe the resultant orcombination of the amplitude pulsations produced by the several different frequencies employed. In case the low frequency currents are o f sine wave form., the' resultant amplitude pulsations wlll be proportional to the sum of the several sine waves employed. VIii'receiving messages sent in this way, an antenna may be employed, which is tuned to the frequency of the source of supply. In conjunction with this antenna, a secondary receiving circuit may be employedl for each message, each secondary circuit being tuned to the particular frequency of the amplitude pulsations which are employedfor transmitting the message to be received in that circuit. In this way f the resultant wave produced by the combination ofthe amplitude pulsations of'several different frequencies may be resolved into its priginal low frequency components.

without interference from a foreign station, the message maybe transmitted simultaneously by means of amplitude pulsations of several different frequencies. The receiving operator may be provided with means for receivingr the message at any one of the amplitude pulsation frequencies transmitted. In order to prevent theproper reception of the message-under these conditions, itwould be necessary .for a disturbing station to set up a wave having amplitude pulsations of the same nature as those produced by the transmittingystation This would be prac- -regular order. In order to receive a message transmitted in thisv way, it will be necessary that the receiving instrument be connected successively in the same order to circuits tuned to the different frequencies used for `producing the amplitude pulsations. It will be evident that it would be practically impossible for a station which was not informed of the different frequencies employed In case it isdesired to transmit a message and of the order in which they were used to Aarrange its receiving `apparatus in such a characteristic of my invention are set forthv with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, to gether with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawings, in which'Fi'g. 1 is a diagrammatic representa: 'tionof a transmitting circuit which may be employed for multiplex operation;v Fig. 2 shows a receiving circuit for the system shown in Fig. l; Ifig. 3`shows a transmitting circuit which may beV used 'for preventing interference; lig. 4 shows a receiving circuit for the system shown in'Fg. 3; Fig. 5 shows a transmitting circuitwhich may be used toinsure secrecy; and Fig. 6 shows a receiving circuit forthe system shown in Fig. 5. Y

As indicated in Fig. 1,'3the antenna 1 is supplied with radio frequency current from any convenient source. For the purpose of illustration I have shown it as supplied by the high frequency alternator 2 through the usual transformer 3. -The alternator 2 may be drive-n by a direct current motor 4 mounted. upon the same shaft 5 and supplied with.k

current from the mains 6.` Connected in shunt to .,the secondary -7 of transformer 3 is a magnetic amplifier comprising a`suitable core 8 of magnetic material and'two windings'9 and 10 as indicated. These windings are so arranged that the high frequency current supplied by vsecondary 7 iiows through the'two windings 9 and 10 )in parallel and that. the flux produced by 4this current flows in opposite directions through the'portions 11 'and l2 of the core 8.

The current for controlling the magnetic amplifier may conveniently be obtainedfrom spect to the high frequency source and hence,

v there is no tendency for high frequenc current to flow through the circuit whic supplies direct current to the windings 9 and 10. The condensers 17 and 18, which are in series with eachv of the windings 9 and 10,

prevent the short circuiting of the direct cur- Arent circuit.

The arrangement thus fardescribed will supply to the antenna continuous radio frequency current of a definite constant amplitude. In order to vary the amplitude of the antenna current, it is only'necessary to vary the controlling current in windings 9 and l0,

-which is supplied frointhe generator 13.

l2 and the motor 4, there may be mounted three alternators 19, 20, and 21. Iloles 22, 23 and 24 yof these alternators are connected directly to the circuit which supplies direct sage transmitted by key 28 will bc transmitted by means of amplitude pulsations having a frequency of 800. Simultaneously a sec-",100 ondmessage may be transmitted by key 29 .by means of amplitude pulsations having a frequency of 700, and a thirdmessage may be transmitted by key B0 by means Aof aml l plitude pulsations having a frequency of 600. The currents supplied by the alternators 19, 20 and'21 should, preferably be of sine wave form in order Vthat the amplitudev pulsations produced may be of a harmonic nature.

The system whichI have described will preferably be so adjusted that when none of thekeys are depressed, about half of the current from the antenna will iow through the windings 9V and 10, and the amplitude of the current flowing in the antenna will be about. 1151 half of the maximum. j When one or more keys are depressed, the controlling current varies and the radio frequency current in windings 9 and 10 will varyaccordingly.

As a result, therev will be a corresponding l variation in the antenna.I current between a maximum and minimum. supplied by the keys is a sine wave alternat-v ing current, the effect will be to produce sine wave pulsations in the amplitude of the current in the antenna. The operation of the control apparatus "may be improved by the use of a condenser 31,v so adjusted that the circuit which includes this condenser and the windings 9 and l0 becomes resonant- 130 e5 lcurrentto the windings 9 and 10, and poles 25, 2G and 27 are connected to that circuit through keys 28, 29 andBO respectively. The

If the current when the` antenna current is a minimum. It will, of course, be apparent that the same effect maybe secured by supplying through the keys 28, 29 and 30 pulsating unidirectional currents of three different frequencies.

In Fig. 2 I have indicated a'simple form of receiving system which may be used for receiving upon asingleantenna all of the' messages transmitted by means of the system shown in Fig. l; The wave having amplitude pulsations may be received upon the antenna 34, which is-tuned to the frequency of the source 2. The received waves are imL pressed uponV the resonant grid circuit.of the electron discharge usual manner, as indicated. In the plate quency of 600 cycles in case the amplitudel pulsations of the different vmessages correspond to these frequencies. In order to obtain a high degreel of selectivity between the different messages, it may be desirable to Acouple loosely to these `tone traps other Vtuned circuits comprising the inductances 43,

44 and 45 and tuning condensers 46, 47 and 48. The coupling may be made through condensers 49, 50 and 51 and receivers, l52,

53 and 54 connected as indicated, may be employed to receive the different messages. With thisarrangement as long as the amplitude pulsations are of substantially sine waveform all confusion between the different messages may be entirely avoided. I While I have described a receiving system in which all of the messages are received at asingle point, it will be apparent that any one of the messages alone may be received at any point desired, and separate messages may be sent from a transmitting station to as many different receiving stations as desired, all by the use of a. single wave length. If the 'received signal is t0 be rendered audible 'the' frequency employed for the `amplitude pulsations Willpreferably be within' the range of audio frequencies, and since the necessary difference between any two of the frequencies employed may be even less than the 100 rcycles which Vis given' in the above eXam le, it is apparent that a large number of iferent messages may be transmittedsimultaneously by a single wave employ a receiver in which the signal vgives a visible'indication, frequencies lower than audio frequencies may be employed for producing amplitude pulsations. It will also be vamplifier 35 in thev length. 'In case it is desired to apparent-that amplitude pulsations o f ultra audible frequencies may also be utilized if desired.

The system which I have described may also be convenientlyv modified for efficienttransmission of messages to different stations located at different distances from the transmittin station. In such a case, the messages` or the nearer station or stations may bev transmitted by amplitude pulsations of a small amount, while the messages for the more distant stations may be transmitted by amplitude pulsations of greater magnitude. This effect maybe obtained by thenuse of variable resistances 55, 56 and 57 in series with the keys 28, 29 and 30 whereby the current flowing through each key may be adjusted independently of the others.

In'Fig. l3' I have indicated an arrangement which is especially adapted for preventing interference with the reception of messages by a foreign station.

In this case .a single key 55 is substituted for the three keys of Fig. 1 so that when this key is operated, amplitude pulsations of three diferent frequencies are produced in the antenna current. The message transmitted may be received-by turning the receiving apparatus to any one of the amplitu'de pulsation frequencies employed for transmission. In case a foreign station sends out a disturbing Wave which prevents the operator from receiving the message at one frequency, he may change over toah.- other frequency for receiving, and unless the disturbing station was informed of all of the different frequencies employed for pro- -ducing amplitude pulsations, it would be practically impossible for it to send out a wave which would interfere with reception at all 'of the different fre uencies employed. In Fig. 4 I have indicate a convenient arrangement' for receiving, in which a single receiver 56 is employed and a switch 57 is provided, whereby the receiving operator can quickly change from one receiving circuit to another. p

In Fig. 5 I have indicated a transmitting system which is especially adapted for sending messages in such 'a way that they can be received only'` by a desired station. In this case each message, instead of being transmitted by means of amplitude pulsations of a definite frequency, is transmitted by means of amplitude pulsations of different frequenc'ies coming one after another in a prearranged regular order. `In order to secure this result, the brushes 25, 26, and 27 may be connected by means of brushes 58, 59, and 60, to three slip rings 61, 62 and 63 respectively. 'All of these rings are arranged to `rotate together -and each ring is'connected to a segment of 4a fourth ring made u of three segments insulated from each ot er. Brushes 65, 66 and 6.7, which are connected Vthe saine segment.

evident that with this arrangement, the

pressing of key 28, vfor example, to transmit a message will produce in the antenna cur- 4rent amplitude pulsations ofrthree different frequencies succeeding each other in regular order and thatV other messages may simultaneously be transmitted by keys 29 and 30 in a similar manner. In order to receive messages sent iii this way it will be necessary to have at the receiving station another set GSof revolving rings, as indicated in Fig-6,

which are driven in synclironisiii with the set at the transmitting station. By this means the different receiving circuits may ,be connected atrthe proper time to the right receiving instrument for receiving each message. It will be apparent that in order to receive a message which is sent in this way, the receiving operator must know the order in which the different amplitude pulsations succeed each other, the frequency of each set andthe speed at which the revolving rings are driven. It would be practically impossible for anyone who was ignorant of these factors to'v receive-any one of the messages transmitted.

lVhile in the above description I have set` forth certain ways in which asystem of transmitting signals by means of amplitude pulsations in continuous radio frequency Waves may be employed, I do not wish to be' l'ii'iiited to the particular'uses described or to the precise circuit connections which I have shovvn, as it will be apparent that many modifications may be made in the manner of. using my invention without departing from the scope thereof, asset forth in theA appended claims.

VVha't I claim as new anddesire to secure by Letters Patent of the United States, is

l. `The method of' radio signaling which consists in producing a continuous radio frequency current in a radiating system,

i transmitting a single signal by simultaneously producing amplitude pulsations of -sine wave form of 'a plurality of different q en. y 1,426,944

frequencies, all of which are'below radio frequency, receiving the wave thus trans= iiiitted and producing an indication of the signal transmitted by selecting from the wave thus received any desired one of vthe different frequencies of amplitude pulsa-v tions. .2. The combination in a radio signaling system of an antenna, a source of continuous radio frequency current connected thereto and meansA for simultaneously producing ,amplitude pulsations in the current in said antenna of a plurality of different frequen-l cies below the radio frequency, andtransmitting a single signal thereby which may be received by selecting any one of said amplitude pulsations, and means at a receiving station for receiving the transmitted Wave, and selecting therefrom any desired one of the different frequencies of. amplitude pulsation 3. The method of controlling the current i in an antenna supplied withV a source of continuous radio frequency current and having a magnetic amplifier associated therewith, which consists in simultaneously supplying to the windings of said amplifier control-ling currents of a plurality of diderent frequencies, all of which are of a frequency lower than that of the source, and thereby producing amplitude pulsations of a. plurality of different frequencies in the current in said. antenna and transmitting a single signal thereby which may be received by selecting any desired one of the different frequencies of amplitude pulsations. l

4. The combination in a system for trans mitting radio signals of an antenna, a source of continuous radio frequency current oonnccted thereto, a magnetic amplifierA comprising la magnetic core having windings thereon, which are associated with said antenna and supp-lied with current there@ from, and means for simultaneously supplying to said windings alternating currents vof a plurality of different frequencies, al1 of which are of a, frequency lower than 'that of the sourceV and transmitting a single signal thereby which may be received by selecting any-one of the amplitude pulsations.,

Inwitness whereof, I havelhereunto set my hand thisfirst day 'of September, 1917.

ERNST IF. W. LEXANnEnsoN. 

